1. Field of the Invention
The present invention relates to a printing method using an ink drum around which a master is wrapped and a system therefor and, more particularly, to a printing method using a plurality of ink drums each being loaded with a respective master for effecting multicolor printing and a system therefor.
2. Discussion of Background
A stencil printer extensively used today includes an ink drum around which a master is wrapped. The stencil printer may be implemented as an automatic digital stencil printer including a single replaceable ink drum. This type of stencil printer wraps a master perforated, or cut, by a thermal head in accordance with image data around the ink drum, and feeds a paper to a nip between the ink drum and pressing means at a preselected timing for thereby printing an image on the paper. The paper with the image, i.e., a printing is driven out of the printer by paper discharging means. The used master is removed from the ink drum by master discharging means.
To produce a color printing or similar multicolor printing with the above digital stencil printer, it is necessary for the operator to replace the ink drum color by color. For example, to produce a bicolor printing, the operator must accurately position a stack of papers carrying images of first color produced with an ink drum of a first color, again stack them on a paper feed section, replace the ink drum with an ink drum of a second color, and repeat printing. While images of the second color must be brought into register with the images of the first color, it is difficult to accurately position the papers fed at the second time, often resulting in misregister. Further, when the images are not fully dry, it is likely that the papers jam a transport path due to the viscosity of ink or that ink deposits on, e.g., rollers arranged on the transport path and smear images printed on the following papers. Moreover, to produce an image in two or more colors, the above procedure must be repeated, consuming a prohibitive period of time and multiplying the above problems.
To solve the problems particular to the single drum type stencil printer, Japanese Patent Laid-Open Publication Nos. 3-55276 and 6-32038, for example, each proposes a plural drum type stencil printer including a plurality of ink drums each being assigned to a particular color. With the plurality of ink drums, the stencil printer continuously prints images of different colors on a single paper one above the other while automatically conveying the paper.
The plural drum type stencil printer allocates exclusive master discharging means, master making means, master feeding means and so forth to each ink drum, as shown and described in the above Laid-Open Publication No. 6-32038. This type of printer is, however, greater in size than the single drum type printer because it needs a plurality of ink drums, e.g., three or four drums in the case of color printing. Moreover, the master discharging device, master making device, master feeding device and so forth allocated to each of the ink drums further increase the size and cost of the printer. This is contradictory to the increasing demand for, e.g., downsizing required of office automation equipment.
In the stencil printer taught in Laid-Open Publication No. 3-55276 mentioned earlier, master discharging means, master making means, master feeding means and so forth are constructed into an integral unit movable to cope with a plurality of ink drums. That is, the single movable unit is shared by a plurality of ink drums. However, to move such a unit, the construction and control of the printer is sophisticated. In addition, although the above means are shared by the ink drums, a space for allowing the unit to move must be provided around each of the ink drums and obstructs downsizing.
Another problem with the printer of Laid-Open Publication No. 6-32038 is that registration errors between masters are not avoidable due to the independent means. For example, even when a document is sized 200 mm, a master of first color and a master of second color may be sized, e.g., 200.3 mm and 199.8 mm by way of example. It is therefore necessary to control the dimensions of the masters to be fed to the respective drums to 200 mm. Moreover, the master of first color and the master of second color may be respectively +0.3 mm and xe2x88x920.1 mm as to the top-and-bottom registration. This must be adjusted also.
Even the printer taught in Laid-Open Publication No. 3-55276 cannot avoid errors relating to the movement of the single unit, also resulting in errors in registration.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication Nos. 7-17121, 8-216381 and 9-104158, and U.S. patent application Ser. No. 09/079,287 (corresponding to Japanese Patent Application No. 9-131428).
It is therefore an object of the present invention to provide a printing system enhancing a low cost, downsizing feature and insuring highly accurate registration at the time of master feed, and a system therefor.
In accordance with the present invention, in a multicolor printing method, a plurality of removable ink drums replaceable with each other are fed with respective masters by fixed master feeding devices smaller in number than the ink drums via the replacement of the ink drums and are used for printing.
Also in accordance with the present invention, in a multicolor printing method, after a master has been wrapped around an ink drum by a master making device including a master feeding function and a master discharging function, the ink drum is mounted to a multicolor printing device capable of accommodating a plurality of removable ink drums, but void of a master making arrangement including a master feeding function and a master discharging function, and used for printing.
Further in accordance with the present invention, a multicolor printing system includes a master making device capable of feeding a new master and discharging a used master and allowing an ink drum to be removably mounted thereto, a multicolor printer loaded with a plurality of removable ink drums, but void of a master making arrangement including a master feeding function and a master discharging function, and a plurality of ink drums shared by the master making device and multicolor printer.
Moreover, in accordance with the present invention, a multicolor printing system includes a plurality of removable ink drums replaceable with each other and capable of implementing simultaneous multicolor printing, a fixed master feeding device shared by the plurality of ink drums, and at least one master discharging device.